I recently purchased two Kingston 2GB sticks of DDR2 RAM to replace my one stick of 1GB DDR2 RAM. So I removed my 1GB stick and replaced it with a 2GB stick and put another 2GB in the empty slot. But my computer refused to boot up. So I switched out one of the 2GB with my old 1GB and it works perfectly, even says that both sticks (the old and one of the new) is working OK. so i switched out the 2GB with the other 2GB and it still worked fine. The computer only had problems when both of the 2GB sticks were in. Why would this be?